The present invention relates to the field of AM stereophonic broadcasting and more particularly to a system for the transmission and reception of a carrier signal bearing information relating to one program signal on a first set of sidebands and, on a second set of sidebands, information relating to a second program signal.
Many systems have been devised for the transmission of two separate program signals on a single, amplitude-modulated carrier. For such a system to be compatible, i.e., to provide reception by a standard monophonic receiver with no added distortion, the receiver typically utilizing envelope detection, it is necessary that the envelope of the transmitted carrier contain only monophonic information, usually expressed as the sum signal (L+R). Therefore, the stereo separation information must be carried by the phase or frequency of the carrier. This variation or modulation of the carrier frequency or phase should be done without causing distortion in monophonic or stereophonic receivers and without degradation of either signal in S/N ratio. One method of doing this is to transmit on one set of sidebands the information necessary to decode the L signal, and on the other set of sidebands the information necessary to decode the R signal.